1. Technical Field
The present invention relates to maintenance of network units, and particularly, but not exclusively, to graceful shutdown of units in intelligent networks, particularly intelligent networks known in the art as Advanced Intelligent Networks (AINs).
2. Related Art
In an AIN, when it is decided to take a service control point (SCP) out of service, the known methods cause that SCP instantly to disable its message input/output subsystem, with the result that transactions that are currently being processed by that SCP, and their associated service switching points (SSPs), cannot complete their normal message sequences, and are left to timeout in the absence of expected response messages.
Not only are SCPs involved in relatively short-term transactions for, e.g. Number Translation services, where an SSP sends dialled digits to an SCP and requests translation to a network destination number, but they are also involved in relatively long-term transactions of many minutes. In the example of queuing of calls to agents at a call centre when all agents are busy, for each new call made to the call centre, the SCP requests the SSP to connect that call to a voice response unit (VRU), which plays out music. Such a call connected to the VRU is given a new transaction and the SCP requests the SSP to arm for “Disconnect, Notify and continue”, as is known in the art, so that the SCP will be told if the caller clears and thus be able to terminate the corresponding transaction and delete that call from its list of queued calls. When an agent becomes free the SSP notifies the SCP and that transaction ends. The SCP then selects a queued call and requests the SSP to disconnect the caller from the VRU and connect that call to the free agent. The transaction for that call remains open until the call ends. Thus for calls to a large call centre the SCP could be maintaining many tens of transactions in respect of queued calls at any one time. In another example, the SCP maintains transactions after call establishment, for calls where the parties can invoke one or more special services, such as call transfer.
Thus, for those known methods, not only will there be failure of calls where, e.g. an SCP is managing a queue, but special service requests would fail. There is thud considerable potential for annoyance to many customers.